1. Field of the Invention
The present invention relates to the art of energy-technological processing organic solid fuels, and particularly to the design of heat exchangers in which the heat transfer is accomplished from a dense gravity layer of bulk materials.
The invention may prove most advantageous when used in energy-technological lines for the heat treatment of oil shales of fine fractional compositions.
2. Prior Art
Due to the ever increasing fuel consumption, oil in particular, and resulting decrease in resources of quality fuel, more and more attention is paid at present to the utilization of fuels having low heat of combustion.
It is well known that the shortage in valuable fuels can be compensated by means of thermal or energy-technological processing low-quality fuels. Such fuels may be brown coal or oil shales.
It is known from the experience of thermal processing oil shales of fine fractional compositions that in the process of fuel treatment a great amount of ash is continuously emanated. Generally the amount of this ash is about 30 to 40% based on the mass of starting fuel, the initial temperature of said ash being of about 800.degree. C. Naturally, such a temperature potential is to be used, i.e. the heat of ash is to be utilized. However, those skilled in the art of power engineering have been engaged up to now mainly in the problem of heat treating solid fuels. At present, due to the expansion of scale of treating oil shales in particular, the problem of utilization of the heat of ash thereof has arisen.
However, in the practice of energy-technological processing fuels, heat exchangers for the commercial utilization of the heat of fine fractional ash within a dense gravity layer are not known.
The use of conventional heat exchangers to solve this problem is difficult since such heat exchangers are designed as a rule to be utilized with gaseous or liquid heat carriers. The difficulties are caused by a high pressure and temperature of the ash, and by the necessity of the provision of a uniform distribution of the ash flow during its motion within a dense gravity layer. The complexity of utilization of the prior art heat exchangers further consists in that they cannot withstand high pressures and operate in an energy-technological line to accomplish preliminary heating of air which is to be supplied under high pressure directly to the fuel processing apparatus.
Known in the art is a heat exchanger (U.S. Pat. No. 3,483,920), comprising a vertical cylindrical container provided with upper and lower end walls, a heating surface disposed inside the container and formed by a tubular perforated housing opened at the lower end and a plurality of tubes mounted therewithin in tiers, said tubes being so disposed that the tubes of one tier are transverse to those of adjacent tiers, opposite seals mounted between the inner surface of the container and the outer surface of the housing so that they divide the cavity of the container along the whole height thereof into two portions, an inlet for one type of the heat carrier inside the housing, an inlet pipe for the other type of the heat carrier to be supplied into the space provided between the inner surface of the container and the housing, and an outlet pipe for discharging the second type of the heat carrier.
The opposite seals of the housing are formed by W-shaped holders extending along the whole height of the container. The W-shaped holders contact with recesses thereof with the housing edges.
For the purpose of changing the direction of motion of the heat carrier passing through the pipes of the heating surface, the tubes having similar location are connected therebetween by means of elbows.
In principle, the above described heat exchanger may be used for the utilization of the ash heat, though its application in the commercial energy-technological lines faces some difficulties.
Thus, in the above described heat exchanger the heat carrier which can be air, in the process of motion over the heat exchanger and passing through the tubes of the heating surface, flows along the shortest path, i.e. from the inlet to the outlet. Due to such an arrangement, some "shaded" regions or regions located out of the shortest path are formed within the container. The heat exchange in such regions is lowered, thereby decreasing heat removal.
The attempts of elimination of the "shaded" regions by coupling, using elbows, similarly directed tubes lead to other difficulties. Thus, when using a gaseous heat carrier, the diameters of tubes and coupling elbows are to be increased. This results in a drastic increase in the metal content of the structure, requires the solution of a complicated problem of thermal expansions, and finally causes a significant complication of assemblying the heat exchanger. On the other hand, if the velocity of the gaseous heat carrier is increased instead of increasing the diameters of the tubes, such an increase will result in a considerable growth of aerodynamic resistances. This requires additional power expenditures.
Moreover, tightly sealing the housing by the W-shaped holders eliminates the temperature displacements of the housing relative to the container.